Mechanical Analogies of Series and Parallel Electrical Circuit

Coupling of motor shaft or generator shaft does not help as they operate at characteristic frequencies and speed variations results in change of the frequency of the generator and change in efficiency of the motors. While you can add voltage and current to any limit, you can not add speed and torque freely. Yes something can be added like 10 motors of 1/10 power can drive one generator easily or 10 horses can operate in one cart.

Coupling two motors as you suggest isn't going to increase the output speed - why should it? A motor is not going to want to run any faster just because it's coupled to another, similar, motor turning at the same speed (they present zero differential torque to each other - if there is such a thing ).

In-line or side-by-side with pulleys comes to the same thing here.

To get more speed from the combination (with the same torque as a single motor) you need some gearing.

what you are saying is to make many motors using one shaft going through all motors and in that case it is like one big motor. This stuff may be Ok as long as their force couples well and you get torque multiplier. You will get thinner longer motor than thicker short motor.

In the "series" scenario, if you are using AC motors is it necessary to align the armatures in some fashion so that variations in the AC supply affect each motor in the same way and so that each motor's electrical response be similar? Should DC motors also consider similar alignments so that the commutators, for example, all switch at the same time?

Every one of us agree including me that we can not add two speeds but we can't add forces (torque)

All kind of powers has two ordinates. Like voltage and current, Speed and torque, force and displacements, Mass*specific heat and temp, etc,

But thing that I want to find out is there any way by which we can add the speeds. As, we can add torque or force,

If not then my question is why different types of powers or energies have different behaviors.

Can we find out some scientific logic involved, I think so far all of our conclusions are only instinctive,

If we can't get a logical reason then there must be some alternate way to couple the speeds. But, yet to be discovered,

Please raed "speeds but we can't add forces (torque)" as "speeds but we can add forces (torque)" In my post #6

Here is a thought experiment for you. First, lets remove a few variables--when we say "motor" we are referring to a torque producing device like a DC motor, a hydraulic or air motor, even an internal combustion gasoline engine--doesn't matter. It produces a given twisting power at a given RPM. Lets pretend that they will not change RPM under load (like an infinitely stiff power supply). Obviously if you gang two of them together, output shaft to input shaft (and assuming they both rotate the same direction), you will double the torque available at the second output shaft. The rpms will not change but it would require twice as much braking force (think counter emf) to stall the system. Now, the harder part--envisioning a way to couple them that would double the rpms but not double the torque. You have to let one motor spin the other motor and apply your load to the output shaft of the second motor. Easiest real-world configuration I can imagine would be a standard radial aircraft engine (like an old Pratt and Whitney five cylinder radial) bolted to a stand. Now instead of the propeller on the front end of the crankshaft, bolt the mounting plate of a second identical engine. Your load goes where the propeller would have gone on that engine. Now torque stays the same but rpms are doubled. How to get fuel, air, and ignition into that second engine when it is spinning at 600 rpm is a bit of a deal breaker but the thought experiment works OK.

I think that you could look at this mathematically by imagining a unit lever on the output shaft and comparing force and velocity at a given instant with vector analysis. Force times velocity (analogous to amps times volts) will sum the same in both cases. Or the area under the integral, if you choose to use some calculus. Hope this was fun for you all.

Lon

attaching two engines to the tran are just to add force. you can also do it with four to add torque.

Gearing is a mechanical analogy of electrical transformer. So it can't be compared with series and parallel circuits.

I think scientific answer is given by the guest # 5. Although I doubt that it can be ever engineered.

In Electrical, connecting something in series means connecting negative to positive terminal. Connecting something in parallell means connecting a positive to a positive. It has nothing to do with the physical arrangement whether one is in front of the other or they are side by side.

In a motor, the negative/neutral can be seen as a stator of the motor. The positive is the rotor. If you connect a rotor to a rotor you have a paralell connection which is what you have done. To connect motors in series, you need to mount a stator of motor B on the rotor/shaft of motor A, such that if motor A runs, the whole of motor B rotates. When motor B runs, the rotor of motor B will run at a speed of motor A +B, reletive to the stator of motor A.

Your conclusion sounds me nice.

I don't know why you didn't sign in.

Only thing that need to be answered is practicality of the method you suggested.

If we mount the whole motor on a rotating shaft we will have to incorporate two slip rings too.

Also all the motors as whole is not symmetrical and will create huge vibrations when rotates.

Also shaft of 1^st motor needs to be made very strong to handle the mass of 2^nd motor.

And inertia of the mounted motor will not allow speed pick up,

What do you think?

Seems to me the biggest problem with this scheme is matching the coupling (not necessarily the motor) speeds. That is to say, if two motors drive a common belt directly through a sheave, you want to make sure the sheaves are the same size for the same rpm motors. Otherwise your motors will be fighting each other, with the belt as the loser. If you can sychronize the couplings, there seems to be little in the way of your getting more torque at a given rpm.

If you're using AC motors, it may be worthwhile to use synchronous motors that are in lock-step with some frequency standard. If you use some other kind of AC motor, you can fall victim to manufacturing/design differences which result in speed differences between them. If you must use motors which do not provide an intrinsic control over the speed (as you have with synchronous AC motors) you'll need to synchronize the speeds by some other means; perhaps by embedding each motor inside its own control loop with all the loops slaved to some master speed control. This approach applies to DC motors as well.

Even if two DC motors are of the same design (again in the parallel scheme), they will have minor differences which result in different rpms. Even if you put the motors in series (electrically speaking) so that the same current flows through each motor, the voltage across each motor may still vary depending on a number of circumstances.

For example, one motor's commutator may be switching to the next set of windings while the other motor is not. While the one motor is momentarily "cogging," the other is supplying a reasonably constant speed and torque. Consequently, they'll fight each other periodically via the belt coupling and, again, the belt willl be the worse for wear.

In both the parallel and series motor schemes it is only the torque which increased (all else being equal). Speed is not a consideration, nor is there even a mechanism which has any effect on speed as some function of number of motors coupled. I must admit here that this part of your question is a little ambiguous.

The electrical analog for both scenarios is comparable to an increase of current (torque) at the same voltage (rpm). Perhaps electrically we might compare the arrangement to batteries in parallel. Beyond that, the analogy falls apart. Note that I used 'arrangement' in the singular. The reason that both scenarios apply only to net torque is that these apparently distinct "series" and "parallel" scenarios are identically one and the same scenario. Think about why this might be.

In summary, I'd say the closest electrical analogy to motors coupled in this way is one of batteries (of the same voltage) connected in parallel. No more, no less.

-e

Europium

The only question raised is why only torque is being added in both cases, if we can add two different ordinates in the case of electrical power then why cant in case of mechanical power.

In the cases shown by me it was the only torque which was getting added. This means both are the parallel combinations.

So the ultimate question is what series combination, which can add the RPM,

And I think we have the answer. And is given by guest # 5,

Now if you were to have both those motors drive hydraulic pumps...

you could increase the flow rate [current] or pressure [voltage] & use the output to drive a hydraulic motor.

Air compressers/motors could also be used, w/similar effect.

Belts & pulleys will give you the same effects, having 2x the torque will allow you to turn the same load 2x as fast, because you can change the ratio from 1:1 to 1:2 & utilize the 2x torque. No load analogies don't hold true, because you aren't runnig the system same % of capacity !

Any sort of direct coupling will be problematic [non linear], just as impedence, phase or Hz mismatches will in ac circuits.

if you want to see a practical example of multi engine configurations go and watch some tractor pulling where the top classes have up to 6 big V8 2000HP drag racing engines on a chassis driving the rear wheels through (I think) a hydraulic gearbox. The torque is incredible but no increase in rotational speed.

Some of those tractor-pulls are simply incredible. At one pull, First Prize went to the guy with two nitro-gulping fully-blown Allison V12 aircraft engines running in tandem. It was the loudest G-D'd thing I've ever heard in my life, next to a shuttle liftoff. With thousands of horsepower at his disposal, the guy moved that 50,000-pound "drag sled" 300 feet in 15 seconds flat. Even Art Arfon's jet-engine-powered machine barely made it to Third Place.

By far the best part of the show was when the frontmost blown Hemi in a five-engine disaster totally blew itself to smithereens. Gawd was that cool! I was hit by a piece of tubing the size of my thumb (just a bruise), and it still smelled like fresh nitro.

For your information: this HAS been done many times in the past , where there were more reasons for doing this other than just add power. Added redundancy in critical applications, weight savings when considering aeronautical products etc. One very good and successful example that I can come up with is the 407 Bell Helicopter (I believe it was), that is a twin engine helicopter using single gear box to turn it's rotor blades. It has also been done in hydroelectric power stations, where several turbines are connected to a single shaft as a torque multiplier and many other applications. The main engineering problem in such designs will be the difference in the power intake part where if not equal, the higher power body will start feeding the lower power body, same as with dissimilar batteries, causing loss of power and other problems. I wouldn't discard the idea, but it certainly needs careful design and application analysis.

Wangito.

What you are talking about is all what had been talked so far. Addition of torque,

Find out some example where you are adding speeds.

As it seems your question has already been answered in post #5, why then are you ordering Wangito to come up with an answer? It's your problem, Mister, not his.

How about an alternative approach: Thank Wangito and the rest of this thread for their replies.

If you still don't have a grasp of the fundamental issues by this point, maybe a concerted study of the fundamentals themselves is in order - or maybe you should be investing your energies elsewhere, perhaps on something for which you have more of a natural aptitude.

Regardless, Mister R-S, you're hardly in a position to order other people to solve your problems for you, like you've just done here with Wangito.

How about showing some manners? And showing maybe a little bit of gratitude for others' efforts? "Please" and "Thank you" can work wonders.

Very harsh.

Mr. Guest, # 18, thanks for your write up,

I have sent my apology to wantigo,

but I am sorry to say-

"Good manners can not be taught with harsh words"

Very well said, Guest - just what I was thinking (somewhere deep inside).

Thank you.

An additional application that comes to mind is drag racing. I know they were building dragsters with multiple engines back in the '60s. I've no idea how the power from these engines were coupled to the tires though.

Wantigo,

I apologize, regardless of if it hurts you or not,Content of sentence was bad but intent was not that, any way I take it back, Sorry once again,

rakesh

My apologies also, Mister R-S. My reproach was unnecessarily harsh. Seems I need to work on my own manners before taking offense at someone else's maybe?

at the end we all gain,

SERIES: The front end of one shaft is coupled with THE MOTOR BODY of second shaft. RPM sums and torque is equal. PARALEL: Two motors with shaft in both sides coupled shaft to shaft. Same RPM double torque

Bingo!

Langdom,

Is this what you mean?

Excellent analogy, great thinking!

I think this is the right analogy so far, but very difficult to apply,

Can we find out some application of this analogy? I doubt!

I don't know if some one is applying it in practice or not. But same idea can be applied with pneumatic and hydraulic cylinders.

We can multiply displacement by adding multiple cylinders.

Your picture presentation was really nice.

Using multiple 'pull-type' solenoids can also be useful - the pull force increases dramatically as the armature moves into the coil. I use two in-line coupled solenoids to lift a heavy metal shutter to expose a radiation source. It's used to lift the shutter to make it fail-safe (i.e. it closes under gravity if the power fails). I couldn't get nearly enough force from a single off-the-shelf 24V solenoid with the required stroke.

Its clear now in case of dynamic machines,The potential difference is in between static and dynamic parts of machine regardless of the type of machine. And to add the speeds or displacement one need to couple dynamic part of machine 1 with static part of machine 2.

But another question is, how two carts can be coupled running on the road, to add the speed,

Park them both on a flatbed truck moving twice as fast?

You hit the nail on the head. Two electric motors with shafts coupled together either in line, through common gearing, pulleys, etc, are in parallel -- even though the first alternative appears at first glance to be in series. To put two motors in series, you must, as you said, turn the housing of one with the shaft of the other. It's not that the principle (of getting twice the speed from two motors in true mechanical series) doesn't apply -- its just that the mechanical arrangement is rarely seen.

As I think someone else mentioned, you can also have fun coupling two motors through a differential. For those with time on their hands, grab an old car rear axle, put two motors where the wheels would otherwise be, and watch the pinion as you power the motors in various directions.

A couple more thoughts:

People who live where the roads get icy can verify this: When one drive wheel spins on a car with a conventional differential, it spins at double the "expected" speed for that engine rpm and gearing (assuming the other wheel is stuck is a snow drift). The torque at the wheel is halved (relative to its "normal" value). Back when I was younger and even more foolish, I would do this experiment on a car lift with the engine running. Grab a spinning wheel with bare hands? Sure!

I can't think of an application in which a motor housing is spun by the shaft of another motor -- but I'm sure someone has built such a thing. Grab a couple slip rings from an alternator, stick them on the driven motor, and you're good to go, right?

Planetary gearsets are also fun to play with to get some of the same effects. When a conventional automatic transmission changes ratios, it does so by applying brakes to the housing of one or more planetary gearsets. The transmission functions as mechanical computer, doing additions and subtractions.

Somewhere, I have a book of mechanical computers from the 30's and 40's, many developed under military contract. I wonder if, in the early days of analogue computers, someone might have coupled motors together in series?

Then there is another possibility for series connection in which a motor-generator drives another motor (or generator) through wires rather than through a mechanical coupling. This was once a not-too-uncommmon way of increasing voltage.

Drifting off even further... For crude regenerative braking on a home made electric car, one can use a conventional transmission, and downshift for braking, spinning the motor fast enough to exceed battery voltage.

- "spinning the motor fast enough to exceed battery voltage" -

I reckon you need a bit of regulation in there, somewhere, or the battery'll get just a bit smelly!

If you connect two motors to a common differential using the axel shafts as inputs and the drive shaft as an output, you will get a power output equal to the sum of the motor power and a speed equal to the average of the two motors. That is the mechanical equivalent to putting two capacitors in parallel.

You are all discussing different forms of energy.

Torque vs RPM

Voltage Vs Amperage

These are units that have inverse relationships with each other.

Because in both cases they multiply up to give you POWER.

2 Electrical generators in series or parallel double the electrical power created.

2 motors of any kind in series or parallel will have double the mechanical power of 1.

The method of how the power is presented depends on the situation.

For the electrical case:

It has to do with alternating current and how the math of a sine wave works.

You are trying to make an analogy of two similar but very different situations.

<You are all discussing different forms of energy. Torque vs RPM Voltage Vs Amperage>

Close, but no cigar. The analogies made thus far are clearly drawn between: Torque vs Current, and Speed vs Voltage.

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<For the electrical case: It has to do with alternating current and how the math of a sine wave works.>

How is the math of a sine relevant to the problem at hand? Is it really? Why?

Also, where does the poster actually say that these are electric motors, let alone AC electric motors specifically? Certainly a number of respondants have assumed that these are electric motors, but where does the original poster actually say what they are? Does it matter? Really, all that is required of each "motor" here is that it have a shaft which rotates at some angular velocity and that the motor generate a torque. Come to think of it, the original poster doesn't even say whether the motors are identical!

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<You are trying to make an analogy of two similar but very different situations.>

This is a Bad Thing?

Surely by now you've discovered that such analogies are perhaps one of the better teaching aids ever discovered. Why? Because analogies contrast and compare a known concepts with new or unfamiliar concepts that are basically similar in some way. And as it happens, people tend to learn a new concept faster and better when they almost know it already. This is what makes analogies so effective.

And as your post mentions electricity, how many times have you yourself heard an analogy between electricity and the flow of water through pipes? Current corresponds to, well, current, and voltage corresponds to pressure. People can see water; they can't see electricity. You may even have heard a resistor described as being a fat or skinny length of pipe, depending on whether you're speaking of a small resistance or a large one, respectively.

Two very different situations, yes. An effective comparison? Absolutely!

Yes when we say motor means two ordinates torque and speed. Regardless of types,

I don't know about others, but I am sure I have learnt lot with so many good ideas. Idea, after idea,

Just see the picture; I was searching for thing like that. And I found it at the end. Thanks gentlemen.

Only question to be answered is having ever this analogy used or printed by human. I have never seen, and are there any possibilities to use it.

And how can we couple to carts to add speed. I guess the front wheel of 1^st cart should be deck of 2nd cart. something like this will work!

For better understanding let us use common terms like 'Driver and Driven' instead of 'Motor and Load'.

Case1: A driver runs the driven at a particular speed and load.

Case2: Increased the speed, but load reduced to half.

Case3: Couple the second drive for handling full load at the increased speed.

Obviously gears are unavoidable intermediate elements in most of the machine trains, like transformers in electrical system.

Figure 3 is exact analogy of, two steps up transformer's output coupled in parallel,

There is an electrical analogy to the addition of rotational speeds by rotating the body of the second motor with the shaft of the first.

in the thirties a 1MV AC supply was required for an atom smashing machine, as 1MV transformers were not available a cascade of three 330KV transformers was used with an additional winding on the first supplying the second and a similar arrangement to supply the third

You wrote: "in the thirties a 1MV AC supply was required for an atom smashing machine, as 1MV transformers were not available a cascade of three 330KV transformers was used with an additional winding on the first supplying the second and a similar arrangement to supply the third."

Are you quite sure? Which atom-smasher was this?

In 1930 Cockcroft and Walton used a single 200 kV transformer in their first accelerator. As their first machine couldn't supply protons with enough energy to overcome the repulsive force of an atomic nucleus, they built a new, 800 kV machine, using a 200 kV transformer and a voltage-multiplier stack built from capacitors and diodes. The following is one of their multiplier schematics:

In 1932, C & W's new machine successfully smashed protons into a lithium target, producing alpha particles (helium nuclei).

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Meanwhile, Robert Van de Graaf used an entirely different approach to generate voltages up to 1.5 MV (+750 kV on one sphere, and -750 kV on the other). His design was based on the principles of electrostatics, in which charge was deposited on large, conductive spheres by means of a moving belt. This design did not use a high-voltage transformer at all as the primary supply:

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Originally proposed by Sweden's Gustav Ising, Norway's Rolf Widerõe designed an accelerator which used a relatively low potential to repeatedly accelerate particles to high energies. His design, a type of linear accelerator, proposed using an alternating potential of 25 kV at radio frequencies to incrementally boost particles to higher energies. In his design, positive ions were pulled into a straight cylindrical electrode by a negative potential and then pushed out the other end by a positive potential. By adding more cylinders, each longer than its predecessor to accommodate the increasing velocity of the particles, one could reach higher and higher energies. One of Rolf Wideröe's early designs:

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David Sloan, one of E.O. Lawrence's collegues at Berkely, improved on this design and built a "linac" capable of accelerating particles to over 1 MeV.

Meanwhile E. O. Lawrence worked out the kinks in his "cyclotron," which was based on the same principles as a linac, but which accelerated particles along a curved path inside two flattened, hollow metal cylinders called "dees."

These were the "atom smashers" of the 1930s.

-e

I am of course familiar with all the instalations you illustrate, it was a slip of the keyboard the device of which I wrote was used for lightning simulation

Many thanks for the VdG illustration - I haven't seen it before, and it adds a lot to my (fairly frequent) visits to the Chilton (nr Didcot, UK) site (where the Diamond accelerator thingy is being set up).

As you drive in (towards the HPA-RP (Health Protection Agency - Radiation Protection), fka NRPB (National Radiological Protection Board) buildings), you pass the Diamond project to your left, a tower with a ball on top (the VdG building) to your right, followed by the entrance to the Rutherford-Appleton Labs to your left and the Atlas building to your right.

Further to the right (mostly out of sight from this entrance) is the AEA Harwell site, which was the seat of UK nuclear research & engineering for many years.

The whole site feels steeped in physics & engineering.

You're welcome!

That VdG illustration is highly simplified, as you probably realize. Perhaps this one (of one terminal only) gives a better idea of what's under the hood/bonnet?

I lived some miles north of Boston for a number of years, and one of my favorite treats was to drive into Bean Town and visit the Boston Museum of Science and it's unique Theatre of Electricity. This exhibit features the world's largest VdG generator and if you're lucky enough to show up on a really dry day, expect to see this monster kick some serious butt.

Here are a some current photos of this device and a few historical ones as well. For your viewing pleasure:

1. Not even Dolly has a pair like these!

(Note the comparative size of the operator in his gilded (Faraday) cage. A close look at the picture's foreground reveals a series of vertical wires which serve to protect the audience from the occasional 1.5 megavolt kick in the ass.)

2. "Thanks, Mr. Faraday!"

3. Pay no attention to that 1.5 million volt arc behind the curtain!

4. Putting on the finishing touches. Note the comparative size of the two workers waiting for Gort, who is late for his own wedding.

5. A marriage made in Hell.

6. Fear this, Mr. Tesla!

7. Scientists not included.

-e

Cockroft & walton did not of course have diodes as are used in modern multipiers they used spark caps of graduated lenghts (I am sure they would have loved to have had diodes)

In 1932 Cockcroft and Walton did not have semiconductor diodes, but vacuum-tube diodes and triodes were common. As C & W's accelerator demanded a steady potential, their power-supply design would not have used spark gaps as switches. Possibly you are thinking here of a Marx generator; a high-energy device typically used to deliver short, high-voltage, high-current pulses into a load. C & W's first schematic was used only to illustrate the principle of the thing and used switch symbols for simplicity. The actual multipliers used vacuum tubes exclusively.

C & W's "atom-smasher" accelerated charged particles exclusively by means of electric fields. As the actual flow of ions to the target represented a negligible current - a few microamps at most - it was only necessary for the power supply to deliver a few tens of microamps at the required voltage. Most of this current was due to leakage and not ion current.

Their first multiplier design (see below) featured four vacuum-tube diodes and two triodes (note the absence of circles around the cathode/anode pairs in all the schematics. Vacuum-tube symbols later evolved to include an enclosing circle to denote a sealed envelope). C & W abandoned their first multiplier design in favor of one that used diodes exclusively. In1932, triodes that could withstand 200 kV to 400 kV were simply unavailable. Clearly a different approach was needed.

C & W's second design not only eliminated the triodes, but also reduced to half the voltage seen by the various components. In their final submission to Proceedings of the Royal Society, C & W used two schematics (below) to illustrate both the new multiplier design and the transport of charge between two successive stages in the multiplication process:

Although it may seem this discussion has gotten a bit off-topic, C-W voltage multipliers do parallel the notion of motors being in "series" - the second motor mounted on the shaft of the first, the third on the shaft of the second, etc, although perhaps a better analogy might be one of high-speed elevators atop high-speed elevators.

-e

We have covered a wide field with answers to this one. I think it is a simple question with a simple answer. In a circuit there is resistance so the mechanical system should also have resistance.

Consider that our motor acts against a resistance (say, gravity, as a wagon is pulled up a hill) and the force is transmitted through a continuously various transmission. When the second generator is switched on, the additional output will overcome more of the resistance which will result in an increase in velocity.

Does this sound right?

Bill Morrow

Let us beat this bush with yet another wacky idea.

Imagine a motor with huge air gap. A gap wide enough to accommodate another set of rotor and (rotary) stator.

Now we got a motor in a motor.

We can think of outer motor a speed, say 3000 rpm and inner may have same or different speed, say 950 rpm.

Together they give 3000 + 950 = 3950 rpm.

Reversing the inner, we can get 3000 – 950 = 2050 rpm.

Reversing the outer, -3000 + 950 = - 2050 rpm (in opposite direction?).

Besides their individual speeds: 3000 rpm and 950 rpm by locking one or the other.

If this viable, we can think of composite set of more than two motors in series to get more speeds.

Variable speed motor, without gears?